Preheating start is a necessary important process before an aluminum electrolysis cell enters normal operation. Main effects of the preheating start comprise drying and baking a hearth, melting electrolyte, enabling temperature and depth of the liquid electrolyte to achieve target values, establishing energy balance and material balance and the like. The preheating start is mainly used for providing a necessary operating environment before electrodes enter an operation state.
Traditional common preheating start methods for pre-baking anodic aluminum electrolysis cells comprise coke particle baking, aluminum liquid baking, fuel gas baking and the like. Although the forms of these baking methods are different, anodes need to participate in baking Furthermore, a later-stage management period with high voltage, high molecular ratio and high electrolysis temperature is needed after baking to establish energy balance and material balance, and then the electrolysis cells can be really started.
For the inert electrode aluminum electrolysis cells, as inert electrodes can not directly participate in baking frequently and further need to work in a stable environment, the operation effects and the service life of the insert electrodes can be ensured. The traditional preheating start method for the aluminum electrolysis cell can not be directly used on the inert electrode aluminum electrolysis cell.
In the prior patent documents, the baking start for the inert anodic electrolysis cells mostly indirectly continues to use the traditional methods, in particular to a baking stage.
In the description of Patent Application No. 200510031315.3, an inert anode is contained in a tank body, the tank body adopts a graphite or carbon product, and an electrode after containing is the same as a carbon anode and can be used in baking start or electrode change to avoid the impact of heat, electricity and thermal corrosive gas. The tank body can be consumed away after electrification, and when the inert electrode is exposed, the electrode is naturally transited to a working state.
In the description of Patent Application No. 01820302.7, a plurality of inert electrodes are combined together and insulating material is further added to form the shape which is similar to that of the carbon anode. The combination of each group of inert electrodes can replace one or more carbon anodes in an existing cell. In this patent application, it is disclosed that the carbon anode is firstly used for baking start of the electrolysis cell, and after the operation of the electrolysis cell is stable, the inert anode group is further used for replacement.
In the description of U.S. Pat. No. 6,537,438, when the electrolysis cell is subject to preheating start, a protecting layer is coated outside a cathode. The innermost layer in the protecting layer, which is in contact with the carbon cathode, is a boronizing soft layer, the intermediate layer is metal aluminum or an alloy and the outermost layer is carbon. By adopting a gas baking method, the anode is a metal ceramic anode. The protecting layer of the anode is from the oxidation in the baking process so as to oxidize the surface layer.
It can be seen from these patents that, at present, certain measures are taken for baking start of the inert electrolysis cell, then the traditional baking method can be indirectly adopted and the starting process is not considered too much. A preheating start method for an inert electrode aluminum electrolysis cell was illustrated in the prior patents by the inventors of the present patent application.
Patent Application No. 200910243383.4 provides a preheating start method for an inert anode aluminum electrolysis cell, which is mainly as follows: laying in a hearth electrical heating components (direct current or alternating current power supply) which are consistent with groups of electrodes in number, filling the hearth with electrolyte, heating and melting the electrolyte, and continuously adding the electrolyte to meet the required level. Then, the power of the heating components is reduced, the heating amount of the electrolysis cell in normal operation is simulated and after various technological parameters are stable, inert electrodes are gradually used for replacing heating resistors.
Patent Application No. 201110221899.6 provides a preheating start method for an aluminum electrolysis cell. Heating elements are pre-buried into graphite/carbon electrodes to form preheating electrodes. The heating elements are adopted for heating for an early-stage oven and melting of electrolyte; before the replacement of normal electrodes, direct current passes through the preheating electrodes and the preheating electrodes undergoes electrolysis reaction; and the preheating electrodes are extracted one by one to replace the normal electrodes for operation. The preheating start method can be applied to not only a traditional prebaked carbon anode electrolysis cell, but also an inert electrode aluminum electrolysis cell.
In the above two patent applications, the inventors of the present patent illustrate the preheating start technology for pre-establishing energy balance and pre-establishing an inert electrode operating environment so as to enable the inert electrodes to be capable of operating in a stable environment after electrification. But the shortcomings are as follows: the preheating start method described in Patent Application No. 200910243383.4 is designed for the effects of series electrolysis cells on series current; and after the electrolysis reaction of the graphite/carbon electrode in Patent Application No. 201110221899.6 by passage of a direct current, the graphite/carbon electrode itself can be gradually consumed. On the one hand, it is required to change the graphite/carbon electrodes to be the inert electrodes within a short period of time; and otherwise, the consumption is completed. On the other hand, shedding carbon residue can pollute the electrolyte and is unfavorable for the inert anodes. These unfavorable factors can enable the preheating start process to be non-smooth and produce disturbance on the series electrolysis cells or the electrolysis cell.